1. Field of the Invention
The invention relates to a method for reducing the radioactive material content of fluids withdrawn from subterranean reservoirs or "aquifers" by means of wells.
2. Description of the Prior Art
Naturally-occurring radioactive materials (NORM) are present at varying concentrations in groundwater produced from water supply wells, oil production wells, and gas production wells. In addition, radioactive materials have been artificially introduced into groundwater reservoirs due to leaching or spills associated with radioactive waste disposal, testing, and mining activities. Production of fluids containing radioactive materials poses both health-related and environmental problems. The invention provides a new method of reducing the production of such radioactive materials from wells.
Radioactive materials contained in fluids produced from subterranean reservoirs can pose a significant risk to human health and the environment. Due to toxic and carcinogenic effects, strict health-based limits have been established for human exposure to radium, radon, and other naturally-occurring radionuclides. However, within fluids produced from water, oil, or gas production wells, radioactive material concentrations significantly exceeding acceptable levels are not uncommon. In addition to human exposure, production of such radioactive fluids can contaminate distribution piping and equipment and the environment.
Various water treatment technologies have been shown capable of removing radionuclides from produced fluids; however, such treatment facilities invariably involve generation of a concentrated radioactive waste residue, presenting a significant waste management and disposal problem.
The following prior art patents are directed, generally, to the removal of dissolved contaminants from produced potable groundwater: U.S. Pat. Nos. 3,136,715; 3,449,065; 3,803,208; 3,896,045; 4,054,320; 4,636,367; 4,664,809; 4,804,498.
U.S. Pat. No. 4,664,809, entitled "Groundwater Pollution Abatement" is directed to a method for pollution abatement in groundwaters whereby a series of wells are drilled in the path of the advancing front of contaminants in an aquifer. A particulate absorbent material, such as activated carbon, treated clay, inorganic oxides, silicates, alumino silicates, carbonaceous materials, organic-polymers, and the like is introduced through the wells. While such procedure may treat potable water in the aquifer for various pollutants, these methods are not, however, adequate for removal of radioactive materials from such potable water aquifers.
U.S. Pat. No. 4,054,320, entitled "Method for the Removal of Radioactive Waste During In-Situ Leaching of Uranium" is directed to a leaching process in mining operations wherein a "pre-pack" of sand or other particulate matter is placed around the exterior of the wellscreen of the well through which the leaching water is produced. The sand, or other particulate matter comprising the pre-pack, has deposited thereon a barium-containing ion exchange material designed to extract and concentrate the dissolved uranium contained in the produced waters.
The '320 patent's method may reduce the radionuclide content of produced waters to some degree but poses significant disadvantages relative to the present invention. First, due to the limited sorbent mass provided by the sand "pre-pack", the sorbent capacity of this medium would be consumed in a relatively short period, requiring redrilling of the well and replacement and disposal of the "pre-pack" material. Secondly, the "pre-pack" provides a relatively small surface area for contact with produced fluids. Therefore, radionuclide removal efficiencies would be less than those achieved by a larger in-situ zone that filters out or traps radionuclides in place. Finally, this prior method is intended for use in extraction of uranium ions from leaching fluids used in uranium mining operations, whereas the invention is directed to removing lower levels of radionuclides of concern from water supply wells, oil production wells, or gas production wells.
What is yet needed is a method for treating produced fluids for the removal of radionuclides, including radium and uranium, that is simple, relatively inexpensive, and does not generate a radioactive waste product that poses disposal problems.